1. Field of the Invention
This invention relates in general to the field of fluid spray systems and in particular a control system for atomized air spray apparatus used in conjunction with automatic fluid spraying operations such as spray painting motor vehicles in motor vehicle manufacturing plants.
2. Description of the Prior Art
Control apparatus used for spraying fluids are utilized in many industries and for spraying or applying sundry fluids, each particular use having its own set of specialized requirements. In virtually all of these uses, however, the fluid to be sprayed is first pressurized then atomized or dispersed and then the spray pattern is shaped while being applied. Thus, a control system is required in all applications so that the correct fluid flow and the various operating pressures are achieved.
Industrial paint spraying apparatus used in motor vehicle assembly manufacturing plants is perhaps the most sophisticated of the various types of fluid spray apparatus and control systems in use today. Yet, even such sophisticated equipment and systems are not without need for improvement.
Typically, a prime painted motor vehicle body is carried on a conveyor chain or belt moving at a preselected constant rate of speed past a robotic paint spraying station. There are preset spaces between such motor vehicle bodies so as to result in a preselected length of time between the motor vehicle bodies, depending, of course, upon the rate of speed of the conveyor belt. For automobile bodies, the painting operation lasts approximately 45 seconds with 15 second intervals between the vehicle bodies. The 15 second interval is used to solvent wash the internals of the paint spraying equipment and the lines connected thereto so that another color of paint may then be used to spray paint the next vehicle body approaching the painting station. In this manner, provided the color programming is properly set, motor vehicle bodies may be painted any of the number of colors being used for the particular year and in any sequence.
Typical equipment used for motor vehicle body spray painting includes automatic paint spray guns mounted on mechanical reciprocating apparatus to traverse the spray guns at right angles to the movement of the conveyor. Usually, one such reciprocating mechanism is placed on each side of the motor vehicle body to spray paint the sides thereof and one reciprocating mechanism is placed overhead to spray paint the top of the body. In the prior art, the reciprocating mechanism includes a constant speed motor which drives an endless chain to which the spray gun is attached. A second degree of motion is obtained by another mechanism which allows the spray gun to move perpendicular to the direction of motion of the endless chain, or toward and away from the vehicle body, so as to maintain a relatively constant distance of the spray gun from the particular area being sprayed. The two degrees of motion of the spray apparatus in combination with the speed of the conveyor belt thus allows for spray painting of the contoured body of the motor vehicle. In order to obtain a uniform coating of the paint, it is necessary that the speed of the movement of the conveyor, the speed of the traverse and right angle motion of the spray gun and the spray makeup and pattern produced by the spray gun to be synchronized in a manner such that the uniform coating results. Such operations, in the prior art are accomplished automatically with various types of control mechanism and to activate and deactivate the spray guns.
The spray guns used with the prior art mechanism invariably utilize shop or plant air, suitably pressurized, to control the rate of flow of the paint, the degree of atomization of the paint and the size and shape of the fan, which factors also contribute to a uniform covering. Too little atomizing air causes inadequate atomization which in turn causes drops of paint to be applied to the surface being painted. Too much atomizing air will result in excessive atomization of the paint which will cause it to be deposited in a dry or dusty condition and will cause considerable turbulence blowing much of the paint around the area to be painted. Too little and too much atomizing air, therefore, produces unsatisfactory results. Fan control air, likewise, is an important consideration. For example, if all other conditions remain constant and correct painting was being obtained by using an 8-inch effective fan, and if for any reason the fan diminished to a 6-inch effective size, then instead of a uniform and full application of paint, a "V" striped type of pattern would be applied. Of course, this would be unsatisfactory and require later touchup corrections by manual means. Fluid pressure is an important consideration in that it controls the amount of volume of paint dispensed by the spray apparatus and which is applied to the workpiece. A correct and constant preselected volume of paint dispensed by the spray apparatus is essential to the quality of the end product. Too much paint may run or "curtain"; while, too little paint will result in inadequate coverage. Also, variations in fluid pressure affect the ability of the preset atomizing and fan air pressures to produce the desired effect.
Unfortunately, it is very difficult to independently adjust and control the above parameters with the prior art spray systems due in part to the prior art spray guns, the design of which includes a manual control for adjusting the fan pattern as an integral part of the spray gun, and the manually adjustable control system. For example, assuming that there are 15 different colors being used in a production year, each paint color has its own particular characteristics which require different settings. White paint has much less hiding characteristics than black paint; therefore, more white paint must be applied to adequately conceal the prime painted body than if black paint were being applied. Also, the equipment must be set to deliver the correct amount of paint at a certain width pattern at the correct distance from the workpiece and apply this at a certain gun traverse speed. If the spray equipment is set to apply white paint, the same settings would apply too much black paint which is not only costly but may produce an unsatisfactory result. Although, as stated, the prior art equipment allows for manual adjustment, to a degree, of the paint pressure, fan size, atomizing air flow, etc., the adjustments are difficult, time consuming, not precise nor are they capable of being repeated, and require prepainting tests to assure that the proper settings are achieved. Usually, the integral spray gun adjustments are, therefore, set at a compromise position and the air pressure and flow controls of the control system are set in one position and not thereafter adjusted. The resulting effect is highly undesirable. Too much or not enough paint is applied. The coating is not uniform and there are unpainted areas requiring manual paint spraying corrections. The overall effect is not satisfactory.
Even further, in typical manufacturing plants where shop air is used with the present day spray guns and control systems, the variations in ambient conditions can also affect the ability of motor vehicle manufacturers to produce a consistent high quality painted finish. Temperature and humidity changes within the plant may require more or less paint of a given color, different settings to the atomizing air and different settings to the fan size to optimize the resulting finish. At present, due again to the difficulty of adjusting the spray equipment, such variations are generally ignored.
The inventive spray apparatus disclosed in the above-referenced related patent application overcomes the prior art problems associated with the prior art spray guns. The use of such inventive spray apparatus does not, however, completely solve all the problems of the prior art. Unless properly controlled, even the most advanced spray apparatus cannot in and of itself consistently accomplish optimal results. And, as previously stated, the control systems of the prior art are generally inadequate in achieving optimal results under the numerous and diverse operating conditions and the various variables inherent in the fluid to be sprayed.
With the strong competition from abroad and the high quality of the finish and the paint applied to the imported products, the inadequacies of the present-day spray control systems can no longer be tolerated.
Accordingly, the objects of the present invention include but are not limited to providing a control system for spraying fluids onto a workpiece which control system may be used in different industries for different applications and which permits the attainment of preselected optimal spray parameters to achieve a consistent high quality finish regardless of factory ambient conditions, spray fluid characteristics, and other spraying variables. And, to provide a spray control system which permits simple and effective changes to the system to adjust for any change or deviation from the optimal finish as actually applied regardless of the reason therefor.